In a capacitive sensor, the capacitance of a capacitor is changed by the change of external environment, and a capacitance change signal corresponding to the capacitance change is outputted to sense the change of the external environment. A capacitive sensing circuit is a circuit detecting the capacitance change signal generated by the capacitive sensor. In the case of processing the capacitance change signal as an analog signal, noise cannot be avoided since the capacitance change signal is a low frequency signal. Therefore, the sensing reliability of the capacitive sensing circuit is deteriorated.
Also, in the case of using at least one analog-to-digital converter in order to process the capacitance change signal generated in at least one capacitive sensor as a digital signal, the size of the capacitive sensing circuit is enlarged, and power consumption is considerable since power must be supplied to each of the at least one analog-to-digital converter.